This invention relates to the use of phosphor-based hydrocarbon gelling agents as self-diverting scale inhibitors.
Gelled liquid hydrocarbon fluids have been used in treating subterranean formations penetrated by well bores, e.g., for stimulation or sand control treatments such as fracturing or gravel packing, respectively. In fracturing treatments, a gelled liquid hydrocarbon fracturing fluid that may comprise particulate material, often referred to as proppant, e.g., sand, suspended therein is pumped through a well bore into a subterranean formation at a rate and pressure such that one or more fractures are formed or enhanced in a portion of the formation. Proppant material may be deposited in the fractures to, among other things, prevent the formed fractures from closing, so as to create or maintain conductive channels through which produced fluids may flow to the well bore. At a desired time, the viscosity of the gelled liquid hydrocarbon fluid may be reduced, or “broken”, and the fluid may be recovered.
Similarly, sand control operations, such as gravel packing, use gelled liquid hydrocarbon fluids, often referred to as gravel pack fluids. Gravel pack fluids are often used to suspend gravel particles for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation particulates, to form a gravel pack to enhance sand control. One common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The gravel, among other things, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, among other things, acts to prevent the gravel from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the gravel pack fluid often may be reduced and produced back from the well bore.
Oil-soluble phosphonate compounds, such as polyvalent metal salts of orthophosphonic acid esters have been described for use as gelling agents for forming high-viscosity gelled liquid hydrocarbon treatment fluids. Such gelled liquid hydrocarbon treatment fluids often have included particulate materials such as proppant or gravel, and oftentimes delayed breakers for causing the treatment fluids to break into relatively thin fluids so that the treatment fluids may be produced back. Descriptions of such high-viscosity gelled liquid hydrocarbon treatment fluids and methods of their use are set forth at least in part in U.S. Pat. Nos. 7,328,744, and 6,544,934, and 7,314,850.
Often, subterranean formations and wells that are treated using gelled hydrocarbon fluids contain not only desirable hydrocarbons, but also waters and brines. The handling of such water and brines produced from subterranean formations can present severe scale formation problems. For example, when brines are produced from oil wells that contain scale forming compounds, changes in temperature, pressure and other physical conditions of the brines as they are produced causes the precipitation and deposition of scale in the producing formation, flow lines, separators and other producing and handling equipment. In addition, scale formation can occur when two or more different brines mix. Scale formation on the equipment used to extract oil from the field is highly problematic, particularly on the interior surfaces of production tubing and at the perforations in the wall of the casing itself. Scale formation can greatly reduce the production capacity of a subterranean well.
There are several conventional techniques to counter the problem of oil field scale formation, all of which bear significant disadvantages. The technique of “downhole squeezing” is commonly used, wherein inhibitor chemicals in aqueous solution are injected into the near-wellbore area. A typical squeeze in a well will comprise a preflush, a squeeze pill, and an overflush treatment before the well is returned to normal function. The preflush, which may be comprised of a mixture of surfactant/de-emulsifier solution, stops the formation of emulsions that would block the perforation pores and may wet (with water) formation surfaces. The squeeze pill itself typically involves injection of inhibitor as a 1-20% solution in water, causing saturation of the matrix in a radial area around the well. The overflush comprises a displacement of the squeeze pill that propels the chemical out from the well bore in a wider circumference so that a significant portion of the surrounding surface of rock matrix is exposed to the inhibitor compound.
One known disadvantage to the downhole squeeze method is that when the pressure applied down the well is reversed, a significant portion of the inhibitor chemical is often immediately flushed from the rock. The remaining solution adsorbs to the rock surface and acts to inhibit scale formation by constant treatment as fluid passes through the rock formation into the well conduit. However, over time the inhibitor is gradually washed from the rock surface as fluid production continues until a further de-scaling treatment is required. Another disadvantage is the time and equipment needed to perform the downhole squeeze operation. Another disadvantage is that the squeeze may not be placed in the zones of interest creating an inferior end result.